The present invention relates to the cutting of a subject moving in front of a background so as to make it possible to overlay this subject on a new background.
As is known to the person skilled in the art, a subject moving in front of a background is cut using a signal commonly referred to as a cut key.
The cut key makes it possible to distinguish between the background in front of which the subject is moving, and the actual subject.
The invention provides a novel definition of the cut key, and thereby a novel device for obtaining a cut key according to this novel definition.
In general, the invention relates to any type of electronic equipment employing a novel device such as the one mentioned above.
According to the prior art, it is necessary to calculate the cut key. It is then necessary to define, in the colour space, one or more volumes representing the background in front of which the subject is moving, so as to make it possible to extract the subject from the background.
The key calculation requires the colour space to be separated into three regions: a first region defining a volume representing the background, a second region defining a volume representing the subject, and a third region defining a transition region between the background and the subject.
As is known to the person skilled in the art, the first region, defining the volume representing the background, most often consists of a highly saturated blue colour having a very high degree of apparent uniformity. This means that the band of visible frequencies emitted by the background should be very narrow. This saturation and homogeneity constraint relating to the background in front of which the subject is moving requires this background, and therefore the subject, to be illuminated with a large amount of light. This strong illumination results in veritable problems in terms of visual realism and the quality of the images generated.
It is thus impossible, for example, to overlay a subject illuminated weakly in visible light.
The invention does not have this drawback.